Hibernate 緩存機制
2021-09-18 17:15:36

public class Client
{
    public static void main(String[] args)
    {
        Session session = HibernateUtil.getSessionFactory().openSession();
        Transaction tx = null;
        try
        {
            /*開啟一個事務*/
            tx = session.beginTransaction();
            /*從數(shù)據(jù)庫中獲取id="402881e534fa5a440134fa5a45340002"的Customer對象*/
            Customer customer1 = (Customer)session.get(Customer.class, "402881e534fa5a440134fa5a45340002");
            System.out.println("customer.getUsername is"+customer1.getUsername());
            /*事務提交*/
            tx.commit();
            
            System.out.println("-------------------------------------");
            
            /*開啟一個新事務*/
            tx = session.beginTransaction();
            /*從數(shù)據(jù)庫中獲取id="402881e534fa5a440134fa5a45340002"的Customer對象*/
            Customer customer2 = (Customer)session.get(Customer.class, "402881e534fa5a440134fa5a45340002");
            System.out.println("customer2.getUsername is"+customer2.getUsername());
            /*事務提交*/
            tx.commit();
            
            System.out.println("-------------------------------------");
            
            /*比較兩個get()方法獲取的對象是否是同一個對象*/
            System.out.println("customer1 == customer2 result is "+(customer1==customer2));
        }
        catch (Exception e)
        {
            if(tx!=null)
            {
                tx.rollback();
            }
        }
        finally
        {
            session.close();
        }
    }
}

結果
Hibernate: 
    select
        customer0_.id as id0_0_,
        customer0_.username as username0_0_,
        customer0_.balance as balance0_0_ 
    from
        customer customer0_ 
    where
        customer0_.id=?
customer.getUsername islisi
-------------------------------------
customer2.getUsername islisi
-------------------------------------
customer1 == customer2 result is true

sessionFactory.evict(Customer.class, new Integer(1));  

sessionFactory.evict(Customer.class);  

sessionFactory.evictCollection("Customer.orders");  

<!-- EHCache的配置,hibernate.cfg.xml --> 
<hibernate-configuration>
    <session-factory>
       <!-- 設置二級緩存插件EHCache的Provider類-->
       <property name="hibernate.cache.provider_class">
          org.hibernate.cache.EhCacheProvider
       </property>
       <!-- 啟動"查詢緩存" -->
       <property name="hibernate.cache.use_query_cache">
          true
       </property>
    </session-factory>
  </hibernate-configuration>

<!-- ehcache.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<ehcache>
??? <!--
??????? 緩存到硬盤的路徑
??? -->
??? <diskStore path="d:/ehcache"></diskStore>
??? <!--
??????? 默認設置
??????? maxElementsInMemory : 在內存中最大緩存的對象數(shù)量。
??????? eternal : 緩存的對象是否永遠不變。
??????? timeToIdleSeconds ：可以操作對象的時間。
??????? timeToLiveSeconds ：緩存中對象的生命周期，時間到后查詢數(shù)據(jù)會從數(shù)據(jù)庫中讀取。
??????? overflowToDisk ：內存滿了，是否要緩存到硬盤。
??? -->
??? <defaultCache maxElementsInMemory="200" eternal="false" 
??????? timeToIdleSeconds="50" timeToLiveSeconds="60" overflowToDisk="true"></defaultCache>
??? <!--
??????? 指定緩存的對象。
??????? 下面出現(xiàn)的的屬性覆蓋上面出現(xiàn)的，沒出現(xiàn)的繼承上面的。
??? -->
??? <cache name="com.suxiaolei.hibernate.pojos.Order" maxElementsInMemory="200" eternal="false" 
??????? timeToIdleSeconds="50" timeToLiveSeconds="60" overflowToDisk="true"></cache>
</ehcache>

<!-- *.hbm.xml -->
<?xml version="1.0" encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
 "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
   <class>
       <!-- 設置該持久化類的二級緩存并發(fā)訪問策略 read-only read-write nonstrict-read-write transactional-->
       <cache usage="read-write"/>    
   </class>
</hibernate-mapping>

<hibernate-mapping>
        <class name="com.suxiaolei.hibernate.pojos.Customer" table="customer">
            <!-- 主鍵設置 -->
            <id name="id" type="string">
                <column name="id"></column>
                <generator class="uuid"></generator>
            </id>
            
            <!-- 屬性設置 -->
            <property name="username" column="username" type="string"></property>
            <property name="balance" column="balance" type="integer"></property>
            
            <set name="orders" inverse="true" cascade="all" lazy="false" fetch="join">
                <cache usage="read-only"/>
                <key column="customer_id" ></key>
                <one-to-many class="com.suxiaolei.hibernate.pojos.Order"/>
            </set>
            
        </class>
    </hibernate-mapping>